MDI

Ad Lib MIDI
Developer:	Ad Lib, Inc.
Header:	SMF
Content:	Notational
Instruments:	Internal
Target Output
Released:	1989-05-08
First Game:	?
Extensions	*.mdi

The MDI format was created by Ad Lib, Inc. to upgrade from MUS (AdLib) format. It uses the MIDI structure but designed to work with OPL2 sound chip that allow it to store instrument data and change modes.

Because the format is so similar to MIDI, some MIDI players are able to play the files, though they won't utilize the instrument data or set the song into the correct mode, so the song won't sound correct. The players which can play MDI files correctly are listed below.

Players

(Category)

• MIDI Play - DOS
• Multi Media Machine - DOS

Converters

(Category)

? to MDI

• ROL to MIDI - DOS - ROL

Games

(Category)

Released	Title	Sample
1990-??-??	Golden Axe (DOS)
1991-??-??	Dark Ages (DOS)
1991-??-??	Prehistorik (DOS)
1992-??-??	Amberstar (DOS)
1992-??-??	Gear Works (DOS)
1992-??-??	Starfire (DOS)
1993-??-??	Ultimuh MCMLXVII (DOS)
1994-08-23	Microsoft Space Simulator (DOS)

Technical

• All MDI files begin with "MThd" MIDI header and contain "MTrk" at the start of the MIDI track.
• The End Of Track "FF 2F 00" event is located at the end of file, but not included in the track.
• Some Note Off events may have only Velocity parameter to trigger the note off.
• Program Change events are not used in the track.

Sequencer-Specific Event Format

These events are used to control OPL-compatible chip.

Delta-ticks	Event	Length	Ad Lib ID	Opcode	Data
00	FF 7F	XX	00 00 3F	XX XX	XX .. XX

Possible Opcodes

Opcode	Meaning	Byte #	Description
00 01	Patch (instrument change)	1	Voice / channel number for instrument
		2 - 29	28 byte array of parameters (see structure below)
00 02	Card mode	1	0 = melodic, 1 = percussive
00 03	Pitch bend sensitivity	1	1 - 12 inclusive

Instrument Structure

Instrument parameters are expressed with the structure, which is identical to the structure for an instrument inside a BNK file:

Data type	Name	Description
MDI_OPLREGS	oplModulator	Register values for the Modulator operator (op 0)
MDI_OPLREGS	oplCarrier	Register values for the Carrier operator (op 1)
UINT8	iModWaveSel	Modulator wave select (OPL base register 0xE0)
UINT8	iCarWaveSel	Carrier wave select (OPL base register 0xE0)

The MDI_OPLREGS structure is defined as:

Data type	Name	Description	OPL base register
UINT8	ksl	Key scaling level	0x40 (bits 6-7)
UINT8	multiple	Frequency multiplier	0x20 (bits 0-3)
UINT8	feedback	Feedback [op 0 only, op 1 ignored]	0xC0 (bits 1-3)
UINT8	attack	Attack rate	0x60 (upper four bits)
UINT8	sustain	Sustain level	0x80 (upper four bits)
UINT8	eg	Envelope gain (nonzero value is on)	0x20 (bit 5)
UINT8	decay	Decay rate	0x60 (lower four bits)
UINT8	releaseRate	Release rate	0x80 (lower four bits)
UINT8	totalLevel	Total output level	0x40 (bit 0-5)
UINT8	am	Amplitude modulation (Tremolo)	0x20 (bit 7)
UINT8	vib	Frequency Vibrato	0x20 (bit 6)
UINT8	ksr	Key scaling/envelope rate	0x20 (bit 4)
UINT8	con	Connector [op 0 only, op 1 ignored]	0xC0 (bit 0, inverted)

Channel Utilization

The channel utilization is the same as in the MUS format, except the music can be composed in both melodic and percussive modes, since the format supports mode switching during playback.

Default Timbre

Player should load default timbre if it isn't loaded by sequencer-specific event before.

Links

• cd.textfiles.com/soundsensations/MISCPROG/AD-PROG/ - Source code (part of the Ad Lib Programmer's Manual).
• swag.outpostbbs.net/SOUND/0066.PAS - MDI2MUS by Colin Buckley (incomplete program source).